B for build > under star menu, top middle, its the furthest to the left.

if you're talking about the campaign level I'm thinking of then it's to the right of where you spawn behind some rock you can dig through if you have a good enough drill (dont remember which tier you need)

Tier 3 drill worked for me, or you can explore to the south-east and you can find your way through the tunnels. If you get to the Info Centre that way, there is a mine you can use to blow out the wall for easy access.